1. Area of the Art
The application concerns a device and method for reduction of cellulosic plant materials to micrometer and sub-micrometer particles which are ideal for enzymatic or chemical hydrolysis into sugars or for direct combustion.
2. Description of Related Art
For the last several decades there have been repeated warnings concerning energy shortages. The general pattern has been for energy prices to spike sharply resulting in an economic downturn which temporarily takes the pressures off of energy supplies. At the same time half-hearted energy conservation measures are established. This results in a drop in energy prices so that rampant consumption resumes and energy conservation and long-term energy planning are completely forgotten. Nevertheless, energy supplies are finite. Best estimates are that oils supplies will be mostly depleted within forty or so years. Even with the discovery of new oil fields and improved recovery from existing fields, this estimate is highly unlikely to be increased even two-fold to eighty years. Thus, baring drastic improvements in efficiency or tremendous conservation efforts, some living individuals who are now alive will almost certainly see the end of a petroleum powered world just as our ancestors not that many generation back saw the end of a horse powered technology. Some have pinned their hopes on nuclear power. Unfortunately, the supply of nuclear fuel is also limited particularly considering the inefficient nuclear reactors now in use. Furthermore, the nuclear waste problem is so critical that our civilization could not safely depend on nuclear energy even if the fuel supply were unlimited.
The picture for other popular fossil fuels is not that much brighter than that for oil. It is estimated that current natural gas supplies will be exhausted in about sixty years. Even if the estimated time is doubled, it would appear that wide spread dependence on natural gas will end in no more than one hundred and twenty years. Coal is perhaps the most abundant fossil fuel; there is thought to be at least a 200 year supply. That means that unless alternative energy technologies are soon developed our civilization will become entirely dependant on coal within the next fifty to one hundred years. Yet coal is the fossil fuel that was developed earliest and was largely supplanted by oil and natural gas because coal combustion is dirty and leaves large volumes of ash. Not to mention the terrible environmental costs of coal mining.
However, it is probably not a shortage of coal that will necessitate an abandonment of coal use. Rather it will be the environmental consequences of continued release of fossil carbon dioxide into the atmosphere. This problem, often called global warming, results from combustion of any fossil fuel. It is just that oil will probably be exhausted before the full brunt of the problem is felt. Global warming is probably not a good term because while overall global temperatures are increasing due to excess atmospheric carbon dioxide, the real problem is not warming per se but is drastic climate change. The Earth's climate is always changing—at one time more rapidly that at other times. For example, during the relatively recent drastic climate change that took place at the end of the ice age, climate change was sufficiently slow that living organisms could either adjust to the new climate or relocate to a more amenable climate. Thus as the glaciers retreated and temperatures warmed “arctic” species adapted to cold moved north or into higher elevations. There is every indication that the climate changes resulting from burning of fossil fuels will be too rapid to allow living organisms to relocate. The result will be extreme loss of species and overall biological diversity with a species extinction rate much higher than the already high extinction rate caused by the spread of our civilization.
Until some entirely new energy source such as fusion is perfected, the best answer to the energy conundrum would appear to be greatly increased conservation coupled with exclusive use of renewable energy sources. Most energy on our planet comes ultimately from the sun. Therefore, solar energy in the form of photovoltaic electricity and solar heating are ideal. However, solar energy cannot satisfy all of our needs. Hydroelectric power and wind generated power are two other forms of renewable solar-based energy. None of these power sources result in changes in atmospheric carbon dioxide. Biomass energy (i.e., wood and other plant materials) may be the ideal complement to solar energy. This may seem surprising because biomass energy is normally obtained through combustion of the biomass, and such combustion releases carbon dioxide into the atmosphere. However, biomass is renewable. If plantations of green plants are grown to produce biomass, the released carbon dioxide will quickly be sequestered in new plant material. Thus, the carbon dioxide is used over and over, and the total level of atmospheric carbon dioxide does not continue to increase, as with the burning of fossil fuels. The real problem is how to integrate biomass energy into our economy. There is presently a marked shortage of wood burning stream trains and wood burning automobiles. Nor is direct combustion of biomass in power plants particularly viable because our electrical generation systems are adapted to use liquid oil or natural gas or even pulverized coal.
There has been considerable effort to produce liquid fuel (primarily ethanol) from biomass. This involves fermentation of sugars derived directly from plant products or indirectly from the digestion of cellulosic biomass. The technology for fermenting directly derived sugars is well established. Unfortunately, the greatest potential source of energy is in cellulosic biomass. The conversion of cellulose into fermentable sugar is difficult and at the present not terribly efficient. Typically enzymes or acids are used to hydrolyze the cellulosic biomass into fermentable sugars. Adequate mechanical pretreatment of the biomass is essential. In some processes the biomass is chemically pretreated and then “exploded” by rapid changes in temperature and pressure. Such processes may create large amounts of hazardous chemical waste. Other processes cook wood chips in acid in devices rather like those used to produce wood pulp for paper manufacturing. To date none of these approaches has proven to be highly successful.
The inventor believes that most of the problems of the present technology can be solved by reducing biomass into sufficiently small particles. The inventor has found that such particles (called cellulosic micropowder) can be readily hydrolyzed into sugars and other organic monomers either by means of enzymes or by means of chemical hydrolysis. Probably because of the very small size of the particle, hydrolytic enzymes are far more effective than they are on cellulosic biomass prepared in other ways. Furthermore, micropowder prepared according to the present invention can be directly burned with a spray-like injector not completely unlike a liquid fluid. The key is to prepare extremely fine and uniform micropowder particles.
There are a variety of small devices (generally called “mills”) that are used to disrupt small samples of a variety of organic and inorganic materials. For example, a cutting mill that uses rotating sharp edges can reduce many materials to the 200 μm size range. A cross beater mill adds crushing action to cutting to further reduce processed materials to the 100 μm size range. Rotor beater, rotor centrifuge and vibrating disk mills can further reduce many materials to a 50 μm size range. In comparison to biomass metals have a crystal structure, so that even small particles are very strong. Nevertheless, the ball mill, a popular industrial machine, is capable of shattering the crystal structure of metal particles into smaller sub-particles at a 5 μm size range (or even slightly smaller). However, the typical ball mill does not generally work well on biomass fiber materials perhaps because the biomass is resilient and generally does not behave in a crystalline manner. This notwithstanding, a ball mill with very small balls is able to achieve some limited disruption of biomass fibers. However, none of these prior art devices are practical at an industrially scale. The amounts of material processed are typically a few grams to a few hundred grams. Furthermore, many devices that depend on “cutting” employ sharp edges that rapidly become dulled by attempts to process large volumes of material.
The inventor earlier developed a system to reduce biomass into micropowder using a combination of mechanical force and water addition. (See WO/2002/057317). The micro-powder produced by that method is readily hydrolyzable into fermentable sugars through action of enzymes. However, that process requires repeated addition and removal of water and prolonged mechanical agitation which increased the energy expenditure needed to produce the micropowder. While the overall energy budget of that process was positive, the inventor has continued to work on the problem until the improved method of producing micropowder disclosed herein was perfected.